The present invention relates to a tire marking method.
In particular, the present invention relates to a method of marking a tire to indicate the taper vector direction and the plane of the radial force first harmonic (RF1H) vector.
Two marks are normally made on each tire coming off the production line: a first indicating the taper of the tire, which corresponds, with respect to the rotation direction and the overall extension of the tire, to the mean of the dynamic forces parallel to the rolling axis of the tire and lying in the tread plane; and a second indicating the radial anisotropy of the tire, and more specifically the point on the tire at which the maximum radial force first harmonic value is located Which point is hereinafter referred to as the "first harmonic high point", and coincides with the out point of the radial force first harmonic (RF1H) vector from the tire.
Whereas the first mark is made on the positively-tapering sidewall of the tire, the second, indicating a radial plane of a vector, is made indifferently on either one of the sidewalls
Indications of this sort are important both when assembling the tire to the wheel rim--to improve wheel balance, the tire is advantageously connected vectorially to the rim so that the respective first harmonic points are opposite--and when assembling the wheels to the vehicle--each pair of opposite wheels must be assembled with opposite tapers.
In tire manufacturing plants, specimens of the tires coming off the curing line are normally sent to a so-called TUO (Tire Uniformity Optimizer) machine, which normally comprises two opposed coaxial spindles rotating about a vertical axis and located on opposite sides of a horizontal roller conveyor for successively conveying the tires laid flat, i.e. with the axis of rotation positioned vertically, and with a given face, normally the one bearing the reference numbers, facing upwards The upper spindle is normally powered and axially fixed, while the lower one is normally idle and movable axially through the roller conveyor to raise the tire off the conveyor and connect it to the upper spindle. When activated, the upper spindle rotates the tire and the lower spindle to enable the TUO to make a series of measurements and determine, among other things, the taper of the tire and the location of the "first harmonic high point."
The TUO normally operates in conjunction with a marking machine comprising a marking head located over the tire on the TUO, and which provides for making, on the upper surface of the tire, a first mark indicating the plane of the "first harmonic high point", and a second mark in the event the tire comprises an upward-directed taper vector. Conversely, in the event of a downward-directed taper vector, the second mark, which should be made on the lower surface of the tire inaccessible by the marking head, is not made, and the tire is either marked by hand or left unmarked--the absence of a taper mark being generally accepted as indicating a taper vector directed towards the lower shoulder of the tire or, in general, towards the shoulder opposite the one bearing the reference numbers.
Whichever the case, the above method involves several drawbacks: the absence of a taper mark may be interpreted wrongly; and marking the taper manually undoubtedly involves the use of skilled labour, thus increasing production cost.